The anisotropy of suprathermal electrons in the Martian ionosphere

作     者：YuTian Cao Jun Cui XiaoShu Wu WenJun Liang RuiQi Fu HaoYu Lu YuTian Cao;Jun Cui;XiaoShu Wu;WenJun Liang;RuiQi Fu;HaoYu Lu

作者机构：Planetary Environmental and Astrobiological Research Laboratory(PEARL)School of Atmospheric SciencesSun Yat-sen UniversityZhuhai 519082China Key Laboratory of Geospace EnvironmentUniversity of Science&Technology of ChinaChinese Academy of SciencesHefei 230026China Center for Excellence in Comparative PlanetologyChinese Academy of SciencesHefei 230026China School of Space and EnvironmentBeihang UniversityBeijing 102206China 

出 版 物：《Earth and Planetary Physics》 (地球与行星物理（英文版）)

年 卷 期：2024年第8卷第3期

页      面：459-471页

核心收录：

学科分类：07[理学] 070401[理学-天体物理] 0704[理学-天文学] 

基　　金：the National Natural Science Foundation of China through grants 42241114,42274218 and 42304166 the B-type Strategic Priority Program No.XDB41000000 funded by the Chinese Academy of Sciences the pre-research project on Civil Aerospace Technologies No.D020105 funded by China’s National Space Administration,the Guangdong Basic and Applied Research Foundation Project 2021A1515110271 the Key Laboratory of Geospace Environment,Chinese Academy of Sciences,University of Science&Technology of China 

主　　题：Mars ionosphere suprathermal electron pitch angle distribution 

摘      要：Suprathermal electrons are an important population of the Martian ionosphere, either produced by photoionization of atmospheric neutrals or supplied from the Solar Wind (SW). This study is dedicated to an in-depth investigation of the pitch angle distribution of suprathermal electrons at two representative energies, 19−55 eV and 124−356 eV, using the extensive measurements made by the Solar Wind Electron Analyzer on board the Mars Atmosphere and Volatile Evolution. Throughout the study, we focus on the overall degree of anisotropy, defined as the standard deviation of suprathermal electron intensity among different directions which is normalized by the mean omni-directional intensity. The available data reveal the following characteristics: (1) In general, low energy electrons are more isotropic than high energy electrons, and dayside electrons are more isotropic than nightside electrons;(2) On the dayside, the anisotropy increases with increasing altitude at low energies but remains roughly constant at high energies, whereas on the nightside, the anisotropy decreases with increasing altitude at all energies;(3) Electrons tend to be more isotropic in strongly magnetized regions than in weakly magnetized regions, especially on the nightside. These observations indicate that the anisotropy is a useful diagnostic of suprathermal electron transport, for which the conversion between the parallel and perpendicular momenta as required by the conservation of the first adiabatic invariant, along with the atmospheric absorption at low altitudes, are two crucial factors modulating the observed variation of the anisotropy. Our analysis also highlights the different roles on the observed anisotropy exerted by suprathermal electrons of different origins.